In the photomechanical process, an image formation system capable of ensuring ultrahigh-contrast photographic characteristics is required so as to obtain satisfactory reproduction of continuous gradation in dot images or reproduction of line images. Hitherto, a special developer called a lith developer has been used for this purpose. The lith developer contains only hydroquinone as a developing agent and in order not to inhibit its infectious developability, the developer must be used at a very low concentration of the free sulfite ion (usually, 0.1 mol/l or less) used as a formaldehyde adduct of a sulfite preservative and at a high pH (substantially, pH of 11 or more), otherwise, desirable properties cannot be obtained. Accordingly, the lith developer is extremely susceptible to air oxidation and bound to a serious defect such that it cannot endure storage over 3 days. Therefore, if the processing may be carried out using a general black-and-white developer by taking the stability of the processing as a primary matter, the stability of the developer may outstandingly be improved. However, the dot quality and the like are disadvantageously inferior to those achieved in the development with a lith developer. Further, U.S. Pat. No. 2,419,975 discloses that a high-contrast negative image can be obtained by adding a certain kind of hydrazine compound to a silver halide emulsion. However, in order to obtain a ultrahigh-contrast (.gamma..gtoreq.10) negative image using a specific example of the hydrazine compound set forth in the patent, a developer having a high pH of 12.8 must be used. The strong alkali developer having a pH near 13 is readily air oxidized and unstable and it cannot endure a long-term storage or use. Of course, if the sulfite ion content is increased, the storage ability can be improved but a large amount of sulfite must be added to sufficiently improve the stability of the developer having such a high pH, which gives rise not only to contamination of the processing solution but also a serious bad effect that the increase in image contrast is inhibited. Accordingly, an image formation system ensuring very high contrast free of the above-described defects as well as satisfactory storage ability of the processing solution has been demanded.
To meet these requirements, U.S. Pat. Nos. 4,224,401, 4,168,977, 4,166,742, 4,311,781, 4,272,606, 4,221,857 and 4,243,739 have proposed a system for forming a superhigh-contrast negative image having a .gamma. value exceeding 10 where a surface latent image type silver halide photographic material having added thereto a specific acylhydrazine compound is processed with a stable developer having a pH of from 11.0 to 12.3. However, this image formation system is still bound to a problem such that a superhigh-contrast image is difficultly obtained in a so-called rapid access processing (more specifically, a very rapid photographic processing allowing from 90 to 120 seconds for the total processing time from the initiation of the processing to the production of a dried film through processings, in which from 15 to 60 seconds are allotted to the development) which stands now in a great need.
On the other hand, with respect to a high-contrast silver halide emulsion, for example, British Patent 775,197 and U.S. Pat. No. 3,531,289 disclose an emulsion of grains formed by adding a rhodium salt. However, the increase in contrast due to the rhodium salt is small (according to Example 1 of the above-described U.S. patent, the contrast of 2.60 was increased only to 3.20) and the blacking density (density max) is lowered if the amount of rhodium is increased. A superhigh-contrast image as required in the silver halide photographic material for photomechanical process cannot be obtained.